The present invention is directed to non-stick coated molds, a process for the preparation thereof and a process for the production of plastics molded parts in these non-stick coated molds, and particularly molded parts made of polyurethane foam.
Plastics molded parts are usually produced in plastics molds (e.g. made of synthetic resin or epoxide resin) or metal molds (e.g. made of steel or aluminium). In order to be able to take out or to remove the molded part or adhering residues of product from these molds after production, in an easy manner which does not leave any residues or cause damage, the mold is generally coated with a mold release agent prior to introducing the raw materials into the mold.
It is well-known that wax-like substances are used advantageously as mold release agents during the production of molded parts, e.g. made of polyurethanes (PUR). These mold release agents are applied in a separate working process, e.g. as pure wax by rubbing or painting onto the mold. Introduction by means of spray application, where the wax is emulsified and/or dissolved in solvents and finely sprayed as an aerosol onto the shape-providing surfaces of the mold, is conventionally and very widely used in order to produce a closed, uniform surface film.
Depending on the type of raw materials being processed and/or the method of production, various contour-sharp and low-residue mold release procedures can be performed with such mold release agents. Very frequently, the mold has to be treated with the mold release agent before producing each individual molded part in order to ensure perfect mold release after production.
The processing techniques which are conventionally used for PUR involve a complex chemical reaction taking place in the mold, in which the PUR components, i.e. the polyol and the isocyanate, react in a polyaddition reaction. Shape-production proceeds in parallel with the progress of the chemical reaction. All the starting materials used, and also all the reaction intermediates, have an effect on the surface of the mold. The PUR molded part being produced exhibits good to very good adhesion to the metals or plastics normally used in the construction of molds, which makes a relatively clean mold release procedure difficult to impossible. Thus, the use of mold release agents, in particular during the mold processing of PUR, is generally essential.
It is well-known that, when producing rigid PUR molded parts, the use of mold release agents is not required when particular active substances (i.e. IMRs, or Internal mold release agents) which lead to an automatic separating effect are added to the PUR raw materials. However, this method can be used only in special cases. In particular, this technology cannot be used when producing flexible PUR molded foams, due to the chemical nature of the agents, so (external) mold release agents have to be used in any case in this sector.
Furthermore, on various occasions attempts have been made to avoid the use of mold release agents by the application to molds of (semi-) permanent coatings made, for example, of polytetrafluoroethylene (PTFE). However, these coatings are not cost-neutral with regard to standard mold release agents. Furthermore, the repair of damaged (semi-)permanent surface films is only possible at great expense and generally cannot be performed on site.
The repeated application of (external) mold release agents to the surface of molds, however, has a number of chemical, technical, ecological and economic disadvantages.                The treatment of molds with mold release agents represents an undesired additional operational expense and additional operational costs in a production process. Depending on the frequency and amount of mold release agent used, high additional auxiliary costs are often produced.        In particular when applying a mold release agent to the surface of a mold in a spray process, effective ventilation of the workplace and effective breathing equipment for the processors are required for occupational health reasons, wherein this involves considerable technical and investment input, particularly in the case of large molds.        Mold release agents require a drying time after application to the surface in order to evaporate the solvent before the raw materials being processed can be introduced into the mold. Otherwise, the solvent left behind interferes with processing of the molded part.        Mold release agents, in addition to the waxes and solvents, very often contain auxiliary substances such as e.g. detergents which have an effect on the physico-chemical progress of shape-providing and reaction during processing of the raw materials and thus can have a negative effect on the resulting properties of the molded part.        The mold release agent is generally applied manually, which leads to an irregular surface and makes precise control of the amount used difficult. If the mold release agent is applied irregularly, residues of the molded part may remain behind, at poorly wetted places on the surface, during the mold release process.        In any mold release process, residues of the mold release agent are left adhering to the molded part and the surface of the mold; over time, a generally irregular build-up of a layer of mold release agent is produced on the surface of the mold. This layer interferes with the accuracy of the contours and forces the user to perform complicated and cost-intensive cleaning procedures which, depending on the situation, sometimes have to be performed at very short time intervals (i.e. weekly).        Molded parts often need a subsequent, and separate, cleaning procedure before further processing.        Residues of mold release agent, in particular when applied by spraying, often lead to severe soiling of the workplace.        
It has now been found that coating the surface of the mold with a coating material which contains nanoscale colloidal silicon dioxide and/or colloidal alkylsilsesquioxane in aqueous/alcoholic suspension leads to mold surfaces which eliminate the disadvantages mentioned above and contribute to substantial simplification of the production of a molded part in a mold.
This (semi-)permanent coating of mold surfaces has the following advantages:                It requires the use of small amounts of the coating.        The application process is time-saving and cost-effective.        The coating is contour-accurate.        Coating of all materials conventionally used when making molds is possible.        Temperature management of the mold is not affected.        It survives a number of production cycles without requiring post-processing. Thus, working time required for removing the mold release agent is saved.        Special workplace ventilation and other occupational health measures may not be required.        The cycle of evaporation and drying times to evaporate the solvent is not required.        The time between cleaning cycles can be greatly extended.        The coating is chemically inert and has no effect on the process for molded part production.        In the event of uniform application, there is no risk of partial adhesion by the molded part.        The coating remains adhere entirely to the surface of the mold.        Subsequent cleaning of the molded part is not required.        There is no build-up of mold release agent residues in the mold.        Touching up damaged coatings is possible on site at low cost.        Soiling of the workplace by mold release agent residues is avoided.        
In addition to these advantages, the coating can be colored which permits (a) simple color differentiation between different molds and/or parts and/or (b) use of a simple visual inspection sample for detecting any surface damage.